How Cranberries Stop Bacteria in Their Tracks

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An old wives' tale might be held up by modern science: New
evidence shows how cranberry juice might prevent or cure urinary
tract infections, researchers say.

Cranberry juice has been touted for at least a century as a
remedy for urinary tract infections (UTIs). Yet doctors
remain divided over whether the fruit is truly effective in
treating UTIs.

The largest analysis to date — a review of 24 studies including
more than 4,400 patients, published in 2012 in the Cochrane
Database of Systematic Reviews — suggests that any positive
effect is minimal at best.

The limited evidence in studies regarding the effectiveness of
cranberries, however, might be the way the fruit is used — as a
drink, or as an extract in pill form, according to McGill
University scientists. In their research, led by Nathalie
Tufenkji, a professor of chemical engineering, they added
cranberry derivatives directly to laboratory dishes growing two
bacteria mostly commonly associated with UTIs,
Escherichia coli and Proteus mirabilis.

The cranberry didn't kill these bacteria, but it did limit their
ability to swim and thus spread.

The researchers' most recent study, appearing in June in the
Canadian Journal of Microbiology, was on P. mirabilis.
This bacterium spreads by swimming in swarms. The colony can be
relatively immobile, but then suddenly grow elongated flagella,
whiplike appendages to propel them to a new region to inhabit.
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Tufenkji's group found that cranberry powder in a petri dish
limited the growth of flagella and rendered the colony nearly
motionless. Moreover, increased cranberry concentrations reduced
the bacterium's production of an enzyme called urease, which
contributes to the virulence, or severity, of infection.

The finding has important implications because P.
mirabilis is the main bacterium behind UTIs
caused by catheters in hospitals. Scientists think that
P. mirabilis can migrate up the catheter into the
urinary tract. So a catheter dusted or infused with cranberry
might prevent infection.

Indeed, a second paper by Tufenkji's group, posted online in
advance of publication in the journal Colloids and Surfaces B,
the McGill scientists demonstrated this is possible.

"We showed that we can embed cranberry derivatives into silicone,
which is a commonly used material to make catheters," Tufenkji
told LiveScience. "Once the cranberry is in the silicone, we
found that it is still bioactive; namely, it still prevents
bacteria from swimming and spreading on the catheter surface."

Tufenkji's earlier work found that chemicals in cranberries
called proanthocyanidins (PACs) similarly hindered the gene in
E. coli responsible for growing flagellar filament.
E. coli is the bacterium most associated with
nonhospital-acquired UTIs. Women in particular can pick up this
bacterium from frequent sexual intercourse; although unlike with
a sexually transmitted disease, the bacteria are usually already
on the woman, [S1] and sexual activity merely
moves the bacteria toward the urethra.

Immobilizing bacteria — rather than killing it —is a good thing,
Tufenkji explained. Bacteria are less likely to develop
resistance to a substance that only is hindering their movement,
as opposed to killing bacteria and preventing them from
replicating.

"The mechanism of action is very different from antibiotics,
which depend on killing the cells," Tufenkji said. "Our work to
date suggests that the bacteria cannot develop 'resistance' to
cranberry."

What happens in the body when one consumes cranberries remains a
mystery. Scientists at the University of Rennes in Rennes,
France, found that compounds in cranberries could block up to 80
percent of E. coli from attaching to the cells lining
the urethra, in a laboratory setting. This study appeared in 2012
in the Journal of Medicinal Food.

Tufenkji stressed that her study doesn't validate that
consumption of cranberries could treat UTIs. Antibiotics remain,
for now, the UTI treatment of choice among most medical doctors.

Christopher Wanjek is the author of a new novel, " Hey,
Einstein! ", a comical nature-versus-nurture tale about
raising clones of Albert Einstein in less-than-ideal settings.
His column, Bad Medicine,
appears regularly on LiveScience.